When used as a catalyst support medium, graphitic carbon nanofibers have been found to exert a dramatic effect on the performance of Fe-Cu (7:3) and Fe particles when such systems were heated in hydrocarbon environments. The catalytic activity of these systems, for the conversion of hydrocarbons, was considerably higher than that found when the Fe-containing particles were supported on either active carbon or gamma-alumina and treated under the same conditions. TEM analysis indicated that this enhancement in activity could not be accounted for by a particle size effect. Other possible explanations for this unusual behavior are discussed.